US2042652A - Transmission system - Google Patents

Description

June 2, 1936.

H. COHN TRANSMISSION SYSTEM Filed Jan. 16, 1934 2 Sheets-Sheet l 89 se g 5 1? FE J2": 2 3 5 EE 3 Irwentor: II 060%,

June 2, 1936. H 2,042,652

TRANSMISSION SYSTEM 2 Filed Jan. 16, 1954 2 Sheets-Shqet 2 Patented June 2, 1936 UNITED STATES PATENT OFFICE TRANSMISSION SYSTEM Iiugo Cohn, New York, N; Y., assignor to Radio Receptor Co. Inc., New York, N. Y., a corporation of New York .The invention relates to av system by which periodic signals may be transmitted to various points and also various programs of music,

speeches, radio broadcasts and the like may also be transmitted to the same variouspoints. The system is so arranged that its use for one type of transmission will not preclude its use for the other type of transmission.

Without intending to limit the invention, but

for the purpose of clearly disclosing it in a simple manner it may be described as applied to a school system. It will be understood, of course, that the invention is not limited to school systems but may be employed in whole or in part in other connections such as hospitals, hotels, auditoriums and other installations,

In many schools there is installed a clock associated with. mechanism for causing signals such as bells or the like in various rooms of the school 2-0.- to be sounded at appropriate predetermined times. It is a purpose of the present invention to associate with such a system a loud speaker at each of the school rooms Where the time signal is sounded or at certain selected ones.

2;- be associated with the system a receiver which maybe a microphone or a radio receiver or a phonograph or the like to bring to the system certain sounds which are to be delivered through the loud speakers. The apparatus in each room 30 may be controlled by a switch which may allow the bell-ringing or signal current to go to it, or which may allow the current from the receiver, which may be referred to as the talking current, to go to it. There also may be associated with the system mechanism or switches by which the talking current may be led to the apparatus in all the rooms or in a group or groups of rooms. There -may also be provided mechanism or a switch preferably automatic in its operation controlled by the program clock for closing the signal circuit for a short time to sound the signals in proper rooms at the times for which the program clock may be set even when the talking circuit is in operation. This mechanism preferably will be such as not to permanently interrupt the talking circuit but to allow it to continue to operate after the signal required by the clock has been given.

53 In the accompanying drawings Figure 1 is a diagrammatic showing of one form of system involving the invention in which the bells or other signalling devices in the individual rooms are operated by drect current or by alternating cur- :rent. Fig. 2 is a similar diagrammatic view of a There may system in which the bells or signalling devices may be operated by alternating current.

In Figure 1 a source of direct current I0 is indicated for operating the various signaling devices, illustrated as bells. This may consist of a battery or any other suitable source. A2 designates generally the apparatus in one room consisting of a signaling device II which may be a bell or other suitable mechanism. In parallel with this in the room All is shown a loud speaker 12. Similarly A3 indicates a room in which is a signaling device i3 in parallel with a loud speaker l4. B2 indicates a room in which is a signaling device l5 in parallel. with a loud speaker l6 and B3 indicates a room in which is a signaling device I! in parallel with the loud speaker Hi. It will be understood that the signaling devices do not operate with the alternating current which operates the loud speakers-and the loud speakers do not operate normally with the direct current which operates the signaling devices. This is I effected by suitable selection and installation as is well known in the art. If the signaling system is direct current the loud speaker may click when the current is made and when the current is broken, and in some circumstances may even buzz slightly; if the signaling sytem is alternating current, the loud speaker may buzz more or less loudly depending upon the frequency but this is negligible and does not impair the usefulness of the system.

PC indicates a program clockwhich together with the other apparatus about to be described may be located at any suitable point in the school.

It may be convenient to place this at some central point such as the office of the principal or convenient thereto. As is usual, the program clock is indicated as having a number of ringing circuits marked l, 2, 3, 4, 5 and 6' so that different bells or different groups of bells may be operated on different schedules andthere is provided an interconnecting board indicated generally by the letter B provided with a plurality of busbars corresponding to the six circuits of the program clock PC. These are so arranged that one or a plurality or all of the signaling devices in the various rooms may be connected to any one of the busbars by plugs, screws, or other means, in the manner well known in the art. In Fig. 1 the plug AZP is indicated in place as connecting the apparatus of the room A2 with the busbar associated with station 2011 the program clock PC. The plug BZP connects the apparatus in the room B2 with the busbar associated with the station 2 on the program clockPC. Likewise the apparatus in the rooms A3 and B3 is connected to the busbar associated with station 3 of the program clock PC by means of the plugs A3? and B3B respectively. Apparatus in other rooms (not shown) may be connected to these or other busbars in ways well known in the art. The dotted lines on the program clock PC indicate connections with the busbars through the program clock to one side of the battery I0. It will be understood of course that these connections are normally open but are closed by the program clock at predetermined times.

Arranged at a suitable place which may be centrally located adjacent the program clock PC and away from the rooms are a plurality of controlling switches one for the apparatus in each room. CA2 indicates a controlling switch for the apparatus in the room A2. CA3 indicates a controlling switch for the apparatus in the room A3. CB2 indicates a controlling switch for the apparatus in the room B2. CB3 indicates a controlling switch for the apparatus in the room B3. Each of these switches comprises mechanism for passing current through the loud speaker by connecting it with the output transformer which is diagrammatically indicated at OT.

Associated with each of the busbars on the board B and located at suitable points which may be adjacent the program clock PC are master talking switches which connect the talking circuit to the busbars and thus to the apparatus roe.

in all of the rooms connected to the busbars. MT2 indicates a master talking switch associated with busbar 2 and controlling the master talking circuit to the apparatus in rooms A2 and B2 both of which are shown connected with the busbar 2. MT3 indicates a master talking switch associated with the busbar 3 and controlling the master talking circuit with the apparatus in rooms A3 and B3 both of which are shown connected with the busbar 3. If desired these master controlling switches may be so arranged that all or a plurality of them may be thrown together and operate for a plurality of busbars.

Associated with the program clock contacts for the various busbars are switches which may automatically close the signaling circuits for the busbars even when the talking circuit is in operation and when the signaling circuit is otherwise open these switches will close the signaling circuit and operate the signals in all of the rooms connected to the respective busbars as long as the program clock PC makes the busbar contact. S2 indicates a solenoid switch associated with the program clock busbar contact 2 so as to operate the signected with the busbar 3 when the program clock contact 3 is made although the apparatus may otherwise be in position for operating the loud speakers by operation of the switch MT3 or CA3 or CB3 etc.

20 indicates a device for bringing into the output transformer OT of a power amplifier or audio amplifier, radio set or phonograph the matter 'which is to be distributed through various loud speakers. The device 20 may therefore be taken to represent a microphone for direct speaking etc. or a phonograph for reproduction or a radio or telephone receiving circuit or the like. The waves from the device 20 are received and suitably transformed in the output transformer 0T for transmission through the system by mechanism and arrangements well known in the art and therefore not necessary to be described in detail here. The amplifier may be omitted if the source of audio energy is of sufficient power to operate the loud speakers of the system.

' In order to clearly indicate the character of the invention the paths and circuits of the apparatus will be described in such a way as to indicate the effects of the manipulation and operation of the various switches.

With the switches in the condition indicated on the drawing it will be seen that when the program clock has closed the contact 2 current will pass through the wire 2| to the lower contact 22 of the master talking switch MT2 to the switch arm 23 of that switch into the busbar 2 and through the plug A2? and through the wire 24 to the lower right hand contact 25 of the controlling switch CA2; through the switch lever 26 the wire 21 to the lower left hand contact 23 and the left hand switch lever 29 through the wire 30 to the signal mechanism II in the room A2 and by the wire 3| to the negative side of the battery. At the same time current will pass from the busbar 2 through the plug B2P and the wire 32 to the lower right hand contact 33 of the controlling switch CB2 through the right hand switch arm 34 and the wire 35 to the left hand contact 36 and the left hand switch arm 31 and by way of the wire 38 to the signal mechanism IS in the room B2 which is connected to the return wire 3|. In a similar way the closing of the contact 3 on the program clock PC will cause the signals l3 and H in the rooms A3 and B3 to be operated through the switches C'A3 and CB3.

When it is desired to operate the loud speakers controlled by busbar 2 such as A2 and B2 the master talking switch MT2 may be operated so as to place the switch arm 23 in contact with the upper contact 39. This causes current from the output transformer OT to pass through the wire 40 to the right hand contact 4| of the switch 7 S2 through the switch arm 42 and by the wire 43 to the contact 39 of the switch MT2 and through the switch arm 23, which is now in contact with 39, through the busbar 2 to the plug A2? and through the wire 24, the contact 25, the arm 26, the wire 21, the contact 28, the arm 29 and the wire 30 to the loud speaker |2 the other side of which is connected. through the wires 3| and 44 to the output transformer OT completing the circuit. At the same time current will go from the busbar 2 through the plug B2P and the wire 32 to the contact 33, the arm 34, the wire 35, the contact 36. The arm 31 and the wire 38 to the loud speaker I6 in the room B2 whence connection is made through the wires 3| and 44 to the output transformer OT.

In like manner the switch MT3 may be thrown to connect the talking circuit to the loud speakers the talking current normally operate the bell or signal mechanism.

It will be noted that in moving the arm 23 of the switch MT2 into engagement with the contact 39 it has been lifted from engagement with the contact 22. The opening at 22 breaks the signaling circuit for the busbar corresponding to the contact 2 as described above. In order to allow for the time signal when demanded by the operation of the program clock PC the solenoid switch S2 has been provided. When the contact 2 is made on the program clock PC current will come from the battery it by the wire 2! to the contact 2 and will pass by the wire through the solenoid S2 and by the wires 35 and 24 to the negative side of the battery. This will energize the solenoid of the switch S2 so as to attract the switch arm 42 to the contact 4? thus for the time being breaking the talking circuit at the contact M. The talking circuit will thus remain open for the short time that the contact 2 is made on the program clock. The closure at the contact 4'! in the switch S2 provides a path from the positive side of the battery through the wires 2! and 2-5 to the contact 4? and the switch lever 22 through the wire 43 to the contact 29 of the switch MT2 and the switch arm 23 to the busbar 2 and thence through the plug AZP and the wire 24 to the contact 25 of the controlling switch CA2; through the switch arm 29, the wire 21, the contact 28, the switch arm 29 and the wire 3i] to the signaling mechanism l i and through the wire M to the negative side of the battery. The signaling mechanism iii in the room B2 will be energized at the same time. The energization of the signaling mechanism will continue as long as the contact 2 is made by the program clock PC and when that contact is broken the signaling circuit will be broken and the talking circuit restored by deenergization of the solenoid of switch S2 allowing the switch arm 42 of the switch S2 to return to the contact 4!. Each of the busbars may be provided with similar mechanism. The master talking switch MT3 and the solenoid switch S3 associated with the busbar 3 have been illustrated and it will be observed that they may be operated to close the talking circuit for the instruments connected with the busbar 3 and allow that circuit to be opened and the signaling circuit closed during the short time when the program clock PC closes its contact 3.

Normally the switches may all lie in the positions indicated in the drawing. It may be desired, however, to operate the signals in some or all of the rooms by manual means and this is provided for in the controlling switches exemplified by CA2, CB2, CA3, CB3, it being understood of course that similar individual switches may be provided for the apparatus which is located in each room of the school or other building. In order to energize the signal il in the room A2 the switch arm 29 of switch CA2 may be moved from the contact 28 to the contact 48. In this condition current will pass from the positive side of the battery l9 through the wire 2! to the wire 49, to the contact 48 of the switch CA2 through the switch arm 29 and the wire 30 to the signal mechanism l l which is connected to the negative side of the battery it) by the wire 3!. It will be observed that this operation of the lever arm 29 of the switch CA2 will have no effect upon apparatus in any of the rooms other than the room A2. Since. the talking circuit to the room A2 when in operation passes through the contact 28 and the switch arm 29 of the switch CA2 it is obvious that upward movement of the arm 29 to operate the signal mechanism II will break the talking circuit at the contact 28 which may be remade when the arm 29 returns to its normal position on the contact 28.

It will be remembered that the master talking switch MT2 connected the talking circuit to all of the loud speakers connected with the busbar 2. Provision is made in the individual control switches CA2, CB2, CA3 etc. to energize the loud speakers in individual rooms without at the same time energizing all speakers connected with the same busbar. For instance, the switch arm 26 of the control switch CA2 may be brought into contact with the contact 59 at the right of the switch CA2. In this condition a circuit will be closed from the output transformer OT through the wire 59 to the contact M of the switch S2, the switch arm 42 the wire 63 and the wire 5| to the contact 59 and through the switch arm 26 and the wire 21 to the contact 28, the switch arm 29 and the wire 39 to the loud speaker E2 the other side of which is connected through the wires 3! and 54 to the output transformer OT. It will be noted that when the switch arm 26 is thus thrown to complete the individual talking circuit it does not interrupt the circuit through the solenoid of switch S2. Thus when the talking circuit through the loud speaker i2 is completed by contact of the switch arm 29 with the upper contact 59 the switch S2 remains free to operate. the signal mechanism II when the program clock PC closes its contact 2. When this happens the solenoid S2 will be energized as before by current coming from the battery through the wire 2i and the contact 2 on the program clock PC the wire 45 to the coil of the switch S2 and by the wires at and M to the other side of the battery l9. At this time the circuit for operating the signal II will come from the battery l9 through the wire 2| and the contact 2 on the program clock PC through the wire 25 to the contact 41 of the switch S2 through the switch arm 42, the wires 43 and 5! to the contact 59 through the switch arm 25 and the wire 21, the contact 28, the switch arm 29 and the wire 39 to the signal device II the other side of which is connected through the wire 3! to the other side of the battery It].

The details of the mechanism for throwing, operating and holding the various switches of the system forms no part of the present invention and is not described since they are well known in the art. It will be observed that the switches represented by S2 are so made that normally the switch arm 42 engages the contact 41 and is drawn from such position and into contact with 41 only while the coil of the switch is energized returning to contact with 4% when the coil is de-energized. In the series of switches exemplified by CA2 the arm 29 is normally in contact with 28 but may be lifted, preferably manually, therefrom and held in contact with 48 the arrangement being such that when it is released it wiH return to contact with 28. The switch arm 25 of the switch CA2 while shown in contact with 25, which may be considered its normal position, may be moved into contact with 59 and preferably may be held or locked into that position and so remain as long as it is desired to maintain the talking circuit closed. When the locking or holding mechanism is released the switch arm 26 should return to contact with 25. In the series of switches exemplified by MTZ the switch arm 23 is normally in contact with 22 but may be moved and held or locked into contact with 39 as long as it is desired to keep the talking circuit closed. When the lock or holding mechanism is released the arm 23 should return to contact with 22.

A variation of the system may be made where alternating current is used for operating the bell or other signaling mechanism and this may con sist of simultaneously applying both signaling and talking voltage or superimposing the signal ing voltage upon the talking voltage when signaling is desired. The way such a system may be arranged and operated may be seen from the diagrammatic fragment indicated in Fig. 2 of the drawings; Apparatus associated with two rooms only is indicated but it will be understood that the apparatus may be duplicated and applied to as many rooms as necessary.

In Fig. 2, A represents the apparatus located for instance in the room of a school comprising a bell or other signaling device 66 placed in parallel with loud speaker 6|. As a means of additional protection a condenser C may be placed in the branch containing the loud speaker although this is not essential and it may be omitted if aproperly designed loud speaker is used or it may be replaced by a current limiting resistor. PC represents the program clock. MT indicates a. master talking switch for the current associated with contact 2. At CA is represented a control switch for the apparatus A and at S is represented a solenoid signal switch. O'I represents the output transformer and AS represents a source of alternating current for operat- 3 ing the bells or other signaling mechanism. The

switches are illustrated in their normal position to connect the bell-ringing or signaling system when the appropriate contact is made in the program clock PC. The path of the current may be traced from the source AS through the wire 62 and the contact 2 on the program clock PC which is connected to the busbar, through the plug AP and the wire 63 to the contact 64 shown at the lower right hand side of the switch CA through the switch arm 65 and the wire 66 to the lower left hand contact 61, the switch arm 68 and the wire 69 to the bell or signaling mechanism 66 the other side of which is connected through the wires 16, H and 12 to the source of I alternating current AS. It will be understood of course that this circuit will be closed only at the prearranged times for which the program clock is set. It will be understood also as many other local signaling apparatus as desired may be connected through and operated from the busbar 2.

In order to transmit matter to the loud speakers 6| in the rooms controlling the busbar 2 the master talking switch MT may be closed. This will close a path from the output transformer OT through the wires 13 and 14 through the closed switch MT and by the wires 15 and 16 to the busbar 2 and through the plug AP and the wire 63 to the lower contact 64 in the switch CA through the switch arm 65 and the wire 66 to the lower left hand contact 61 and through the switch arm 66 and the wire 69 to the loud speaker 6| the other side of which is connected to the other side or" the output transformer OT through the wires 16, H and 11.

It will be noted that this talking circuit closed by the switch MT does not interrupt the signaling circuit described above. It will be obvious then that with the master talking switch MT closed the program clock PC may operate to close the signaling circuit and both signaling and talking circuits will pass through the wire 69 into the apparatus in the room A and by properly designing the apparatus and properly selecting the character of the currents both loud speaker and signaling mechanism may be operated.

It may be desired from time to time tooperate the signaling mechanism 66 independently of the program clock PC and this may be done by manual or other operation of the switch arm 68 of the switch CA. By moving the arm 68 away from contact 61 the talking circuit will be broken and when the arm 68 reaches the upper contact 18 it will close a signaling circuit from the source of current AS through the wire 19,

the contact 18, the switch arm 68 and the wire 69 to the bell or signaling mechanism 66 the other side of which is connected through the wires 16, H and 12 to the other side of the current source AS. The switch arm 68 when released may return to the contact 61.

When it is desired to operate not all the loud speakers associated with busbar 2 but only the loud speaker at A the switch arm 65 of the switch CA may be moved from contact 64 on to contacts 86 and 8| where it may be held or may be locked into position for as long a period as it is desired to operate the loud speaker. The talking circuit in this condition is from the output transformer OT through the wires 13 and 82 to the contact 8|, the switch arm 65, the wire 66, the contact 61, the switch arm 68 and the wire 69 to the loud speaker the other side of which is connected through the wires 16, II and 11 to the other side of the output transformer OT.

It will be remembered that the signaling circuit controlled by the program clock PC as in dicated above passed through the contact 64 and the switch arm 65. When the switch arm 65 is moved from contact 64 this circuit is broken. To provide for the operation of the signaling circuit under the control of the program clock PC when the switch CA has been thrown to close the talking circuit a solenoid switch S is provided. When the program clock PC makes its contact at 2 the signaling circuit from the source of supply AS passes through the wire 62, the busbar 2, the wire I6, the wire 83, the solenoid of the switch S the other side of which is connected to the other side of the source of supply AS through the wires 84, H and 12. The energization of the solenoid of the switch S will cause the switch arm 85 to engage the contact 86 thus closing a circuit for signaling current passing from the source of current supply AS through the wire 62, the busbar 2, the wires 16 and 83 to the switch arm 85, through the contact 86 and by the wire 81 to the contact 86 which is in engagement with the switch arm lever 65. The circuit then passes from the switch arm 65 through the wire 66, the contact 61 the switch arm 68, the wire 69 to the signaling mechanism 66 the other side of which is connected to the other side of the source of supply AS through the wires 16, H and 12.

It will be observed that when the signaling circuit is closed for operation during the time the talking circuit is closed both circuits pass to the apparatus at the room A part operating the loud speaker and part operating the signal mechanism arranged in parallel. The various components of the circuits and instruments may be so designed, installed and constructed that but a very small amount of the signaling current passes through the loud speaker and a very small amount of power from the output transformer is consumed by the signaling mechanisms. In this arrangement the talking circuit is not interrupted for the operation of the signals.

The system has been described as comprising a signaling mechanism and a loud speaker at the various rooms or local stations controlled and operated from the main central station which, as above indicated, may or may not be the office of the principal. No means has been indicated at the individual rooms for controlling or cutting in or out the mechanism but obviously each portion or all of the apparatus in each room may have associated with it switches for connecting or disconnecting it with the system.

In many schools there is already installed a signaling system controlled manually or by a program clock. The modern trend is to install in schools a central radio and announcing system so that from some central point radio may be switched to any room or group of rooms through loud speakers mounted in the individual rooms and the principal or others may address one or more class rooms or the auditorium. Such programs starting either from the auditorium or other points within or without the school, or phonograph music or the like may be played through the various loud speakers. This has ;generally necessitated a second complete wiring system to every room adding considerably to the expense in a new building and making sound installations practically prohibitive in old buildings. The present invention comprises an arrangement by which a sound system may be added without appreciable additional wiring either in new installations or where old signaling systems are already installed and at the same time in such a manner as to give the signal preference at all times over the sound system.

It will be understood that satisfactory operation of the system is dependent upon the relation of the bell or other signaling mechanism and the speakers and their circuits which must be such that the voltage and frequencies required to operate the loud speaker at satisfactory volume will not normally operate the signaling mechanism. The voltage or the voltage and frequencies of the signaling circuit must be such that they will not normally operate the loud speaker nor interfere with nor injure the same.

The system may be varied in numerous ways, such as connecting several bells in multiple with one loud speaker, or several speakers in multiple with one bell, or in any combination desired. The master switch may be in one section, or there may be sub-masters for each program circuit. The system could be made to operate effectively by placing the loud speaker in series with the bell leaving everything else practically the same except for the proper adjustment of the operating voltages. There are of course many detailed variations which can be made in these circuits and still produce an operable system.

The invention has been disclosed in specific forms, but is not confined to the details shown as it may be embodied in other arrangements and in other apparatus.

I claim as my invention:

1. In a transmission system a plurality of signaling mechanisms, a plurality of loud speakers each in parallel with a signaling mechanism, means at a remote point for selectively operating the individual signaling mechanisms, means at a remote point for selectively operating the individual loud speakers, means at a remote point for selectively operating a group of the signaling mechanisms, means at a remote point for selectively operating a group of the loud speakers, a program clock for operating the signals at predetermined intervals, and means controlled by the clock for interrupting the operation of the loud speakers and operating the signaling mechanisms and subsequently restoring the operation of the loud speakers.

2. In a transmission system a plurality of signaling mechanisms, a plurality of loud speakers each in parallel with a signaling mechanism, means at a remote point for selectively operating the individual signaling mechanisms, means at a remotepoint for selectively operating the individual loud speakers, means at a remote point for selectively operating a group of the signaling mechanisms, means at a remote point for selectiveiy operating a group of the loud speakers, a program clock for operating the signals at predetermined intervals, and means controlled by the clock for operating the signaling mechanisms when loud speaker controlling mechanism isin position for operating the loud speakers.

3. In a transmission system a plurality of signaling mechanisms, a plurality of loud speakers each in parallel with a signaling mechanism, means at a remote point for selectively operating the individual signaling mechanisms, means at a remote point for selectively operating the individual loud speakers, means at a remote point for selectively operating a group of the signaling mechanisms, means at a remote point for selectively operating a group of the loud speakers, a program clock for operating the signals at predetermined intervals, and means controlled by the clock for operating the signaling mechanisms when loud speaker controlling mechanism is operated.

4. In a transmission system a plurality of signaling mechanisms, a plurality of loud speakers each in parallel with a signaling mechanism, means at a remote point for selectively operating the individual signaling mechanisms, means at a remote point for selectively operating the individual loud speakers, means at a remote point for selectively operating a group of the signaling mechanisms, means at a remote point for selectively operating a group of the loud speakers, a program clock for operating the signals at predetermined intervals, and means controlled by the clock for passing signaling current through the system when loud speaker current is passing through the system.

5. In a transmission system a plurality of signaling mechanisms, a plurality of loud speakers each in parallel with a signaling mechanism, means at a remote point for selectively operating signaling mechanisms, means at a remote point for selectively operating the loud speakers, a program clock for operating the signals at predetermined intervals, and means controlled by the clock for interrupting the operation of the loud speakers and operating the signaling mechanisms and subsequently restoring the operation of the loud speakers.

6. In a transmission system a plurality of signaling mechanisms, a plurality of loud speakers each in parallel with a signaling mechanism, means at a remote point for selectively operating the individual signaling mechanisms, means at a remote point for selectively operating the individual loud speakers, a program clock for operating the signals at predetermined intervals, and

means controlledby the clock for interrupting the operation of the loud speakers and operating the signaling mechanisms and subsequently restoring the operation of the loud speakers.

'7. In a transmission system a plurality of signaling mechanisms, a plurality of loud speakers each in parallel with a signaling mechanism,

means at a remote point for selectively operating a group of the signaling mechanisms, means at a remote point for selectively operating a group of the loud speakers, a program clock for operating the signals at predetermined intervals, and means controlled by the clock for interrupting the operation of the loud speakers and operating the signaling mechanisms and subsequently restoring the operation of the loud speakers.

8. In a transmission system a plurality of signaling mechanisms, a plurality of loud speakers each in parallel with a signaling mechanism, means at a remote point for selectively operating the signaling mechanisms, means at a remote point for selectively operating the loud speakers, a program clock for operating the signals at predetermined intervals, and means controlled by the clock for operating the signaling mechanisms when loud speaker controlling mechanism is in position for operating loud speakers.

9. In a transmission system a plurality of signaling mechanisms, a plurality of loud speakers each in parallel with a signaling mechanism, means at a remote point for selectively operating the signaling mechanisms, means at a remote point for selectively operating the loud speakers, a program clock for operating the signals at predetermined intervals, and means controlled by the clock for passing signaling current through the system when loud speaker current is passing through the system.

10. In a transmission system a, plurality of signaling mechanisms, a plurality of loud speakers each in parallel with a signaling mechanism, means at a remote point for selectively operating the individual signaling mechanisms, means at a remote point for selectively operating the individual loud speakers, means at a remote point for selectively operating a group of the signaling mechanisms, means at a remote point for selectively operating a group of the loud speakers, a program clock for operating the signals at predetermined intervals, and means controlled by the clock for operating the signaling mechanisms with the loud speaker controlling mechanism in any position.

HUGO COHN.

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